I'm no expert, so let me just say something a little bit encouraging: about two years ago, I gave my wife an ultimatum. I did not actually walk away, but I told her I would if we didn't make changes. I realize that's different from the determination to walk out, but my point is that we made a few big changes in our life, and although our marriage isn't perfect, we're happy being married to each other and leaving never crosses my mind anymore.
It can be done. Decide what you want and be single-minded about it.
